1. Field of the Invention
The present invention relates to flow measurements, and more particularly to blood flow measurements in biomedical diagnostic and research applications, wherein a flow rate is determined from sensed relative changes in the flow resulting from a known introduced volume change in the flow.
2. Description of Related Art
Commonly used methods to measure blood flow in biomedical diagnostic and research applications include indicator dilution, transit-time ultrasound, Doppler ultrasound, electromagnetic, nuclear magnetic resonance and x-ray fluoroscopy principles.
The measurement of blood flow is particularly important during vascular reconstructive procedures. In such procedures, the interventional cardiologist/radiologist attempts to restore blood flow in a diseased vessel, so measurement of the efficacy of the procedure constitutes important feedback. While prior methods have practical uses during specific medical studies and protocols, no method has been developed that has found widespread use during vascular reconstructive procedures.
A well-accepted blood flow measurement technique employing indwelling catheters is the indicator dilution method, often named Stewart-Hamilton methods after the inventors who pioneered this family of methods in the late 19th and early 20th century. In this method, an additional element is introduced into or extracted from the blood stream, or a blood property is changed (the “indicator”). A calibrated sensor placed downstream from the point of indicator introduction measures the absolute concentration of the indicator. Via well known equations one can then derive the volume flow at the point of mixing of the indicator with the blood flow. These methods are widely used for cardiac output measurement using pulmonary artery catheters. The method has not found use during interventional procedures likely because it requires pre-calibrated concentration sensors. The calibration of commonly used sensors such as thermal or electrical is affected by changes in vessel diameter.
Therefore, the need exists for determining flow rate in real time during vascular interventional procedures where catheters may be introduced into the patient. The need also exists for determining flow rate during a medical procedure so that the efficacy of the procedure can be determined, thereby reducing complications and subsequent interventions. The need also exists for determining flow in a broad spectrum of applications, without requiring extensive modifications of surgical procedure or retraining of surgical staff.